1. Field of the Invention
The invention relates to the field of dinnerware, glassware, and chinaware, and in particular to fine stemware. The invention concerns a fine stemware assembly that combines portions of crystal glass and china, rigidly attached in a manner that is compliant as to the differences in thermal expansion properties of the two materials. The stemware includes a bowl, stem and foot portion. At least one of these portions, preferably the foot portion, is china, and another is crystal, preferably the stem portion, which can be integrally formed of glass or lead crystal with the bowl. The dissimilar glass (crystal) and ceramic (china) portions are adhered one to the other by an ultraviolet-curing adhesive which creates a substantially strong adhesion and is substantially translucent when cured.
Fine crystals and china have been extensively used in the manufacture of fine dinnerware, such as stemware. Fine glass stemware is known as crystal, and generally comprises a leaded glass. Glass is a hard, brittle, amorphous material which is usually transparent but may be colored or translucent, being substantially a supercooled liquid that forms a non-crystalline solid. Most glasses fall into the category of silicates (SiO.sub.4 tetrahedron) containing modifiers and intermediates. Fine crystals are made particularly from lead glasses in which PbO is introduced into the vitreous silicon-oxygen glass network. Fine crystals are typically made by converting raw materials at high temperatures to viscous melts that are formed to shape by blowing, pressing, casting and/or spinning. Application of the hot glass melt to a mold or the like also cools the glass and sets the final shape. The formed glass may also be annealed, tempered, densified or compacted by post-forming heat treatments.
Stemware and other glasses are subjected to a range of temperatures in use. The thermal expansion properties of glass normally determine the range of materials to which the glass can be adhered or fused. Thermal expansion also affects the glass's internal ability to survive thermal shock or cycling. Strains and stresses caused by thermal gradients may cause cracks or breakage of the glass. Means adhering or fusing the glass to a distinct glass or to another material for mounting may fail during thermal cycling, depending on the degree of constraint imposed by the external mounting material and the respective thermal expansion characteristics. Crystal typically has a higher thermal expansion coefficient than china, or ceramics in general.
China is a ceramic material which is comprised chiefly of kaolinite (Al.sub.2 (OH).sub.4 Si.sub.2 O.sub.5). China is extensively used in whitewares. Ceramics generally are formed and then fired to sinter adjacent particles, by a high temperature firing process typically in a kiln, to form a china bisque having the desired shape. The formed china is also typically glazed for use as whiteware, and can be decorated prior to or in connection with glazing, by application of colored coating patterns that are set during post heat treatments.
Whereas there are a number of different decorative aspects possible with glass and china, respectively, it would be advantageous if it were possible to employ both materials together and thereby set off the decorative attributes of one with the other. However, previous attempts by the present inventors to produce such a piece of stemware, for example a goblet comprising an integral crystal bowl and crystal stem, and a china foot, have been largely unsuccessful due to the consequences of differences of thermal expansion. Either over the short term or long term, the joint between the glass and china fails or stresses applied to the glass or china result in breakage.
Glass can be joined at a seam or the like by fusing, and low melting temperature glasses or "frit" are known to be useful for fusing, normally at a glass-to-glass seam. The inventors have attempted to fuse crystal and china portions together at a joint located at the lower end portion of a glassware stem and the upper portion of the foot. Fusing would be advantageous since a fused joint is continuous across the joint, i.e., not characterized by a gap or similar visually perceptible feature. However, both glass and china are relatively brittle materials that tend to fail by sudden cracking. Due to this aspect of the crystal and china materials and their thermal expansion mismatch, thermal cycling of stemware with a fused joint causes the formation of strains and stresses at the joint, and in particular in and adjacent the crystal. Upon cooling or with thermal cycling, the materials crack or the crystal-china bond fails.
It would be desirable to bond a crystal substrate and china substrate at a joint which is durable and continuous, thereby forming a stemware assembly composite of crystal and china components. It would also be desirable to combine crystal and china portions of the stemware using a bonding agent at the joint that is similar in appearance to glass or china, preferably substantially translucent or transparent when cured, and which deals with the mechanical problems associated with the different thermal expansion characteristics of china and glass.